1. Field of the Invention
The present invention relates to a liquid crystal display device and a color filter for the liquid crystal display device. In particular, the present invention relates to a liquid crystal display device having a color filter capable of exhibiting excellent color reproduction properties while preventing the electrical properties of the colored layers and the overcoat layer thereof from having an adverse influence on the liquid crystal switching property and to the display device.
2. Description of the Related Art
A color liquid crystal display device is now rapidly propagated especially as an image display device for television and as a terminal display device for computers. The color filter is an important component which is indispensable for realizing the color display of such a liquid crystal display device. In recent years, in response to the increasing demands for enhancing the image qualities of a liquid crystal display device, there have been developed liquid crystal display devices of various new systems wherein the view angle is increased or the responding properties are accelerated. Among them, an IPS system (In Plane Switching system) is expected to be widely propagated because of the excellentness in display qualities in terms of the view angle, the contrast ratio, etc.
However, since the colored layers of color filter exist in the liquid-crystal-driving electric field in the case of the liquid crystal display device of the IPS system in different to other liquid crystal display devices of the twisted nematic (TN) or vertical alignment (VA) system, the liquid crystal display device of the IPS system is accompanied with a problem that the display device is directly influenced by the electrical properties of the materials of the colored layers. As a matter of fact, when the colored layers formed of the conventional materials are employed in the liquid crystal display device of the IPS system, there have been recognized various display failures such as turbulences in the alignment of liquid crystal which originate from the electrical properties of the colored layers or the image burn (a phenomenon wherein an image is permitted to remain in a display screen for a long time) due to deviation of the threshold values of switching.
The electrical properties of the materials for the colored layers mainly depend on the characteristics of pigments to be employed as coloring agents and hence it is fundamentally difficult to avoid the influences of the characteristics of coloring agents. Therefore, when a color filter wherein the colored layers formed of the conventional materials are used is employed in the liquid crystal display device of the IPS system, it is generally practiced to provide the color filter with a protective layer (overcoat layer) which is made of a transparent resin (see JP-A 2004-117537, for example).
Certainly, although it is possible, due to the provision of the overcoat layer made of a transparent resin, to employ the colored layers formed of the conventional materials in the liquid crystal display device of the IPS system, there is still a possibility of generating various display failures even if the overcoat layer is employed. There have been proposed improvements on the materials for the colored layers as well as on the materials for the overcoat layer (see JP-A 2006-113099, for example). Incidentally, it may be conceivable to reduce the quantity of the materials for the colored layers which are a fundamental cause for the display failures in order to secure satisfactory performances of the liquid crystal display device, the reduction in quantity of the materials for the colored layers may lead to the deterioration of color reproducibility.